1. Field of the Invention
The present invention relates to an apparatus and method for allocating Radio Network Temporary Identifiers (RNTIs) for random access in a mobile communication system. More particularly, the present invention relates to an apparatus and method for more efficiently allocating RNTIs in a mobile communication system.
2. Description of the Related Art
The Universal Mobile Telecommunication Service (UMTS) system is a 3rd Generation (3G) asynchronous mobile communication system that is based on Global System for Mobile communications (GSM) and General Packet Radio Services (GPRS), which are European mobile communication systems, and uses Wideband Code Division Multiple Access (WCDMA).
The Long Term Evolution (LTE) system is now under discussion as the next-generation mobile communication system of the UMTS system by the 3rd Generation Partnership Project (3GPP), which is in charge of UMTS standardization.
The LTE system is a technology for implementing high-speed packet-based communication at a transfer rate of up to 100 Mbps. To use the LTE technology, there have been discussed many different schemes including a scheme of reducing the number of nodes located in a communication path by simplifying the network configuration and a scheme of using as many radio protocols as possible in radio channels.
FIG. 1 illustrates a conventional configuration of a next-generation LTE mobile communication system.
Referring to FIG. 1, an Evolved UMTS Radio Access Network (E-UTRAN or E-RAN) 110 includes Evolved Node Bs (ENBs) 120, 122, 124, 126 and 128, and anchor nodes 130 and 132, which are upper nodes of the ENBs 120 to 128. A User Equipment (UE) 101 accesses an Internet Protocol (IP) network 114 by means of the E-UTRAN 110.
The ENBs 120 to 128 correspond to the legacy Node Bs of the UMTS system, and are connected to the UE 101 through a radio channel. The ENBs 120 to 128 take charge of more complex functions as compared with the legacy Node Bs. For example, in LTE, as all user traffic, including real-time services such as IP-based Voice over IP (VoIP), is serviced through a shared channel, the ENBs 120 to 128 perform scheduling by collecting status information of UEs and perform functions related to radio resource management.
The ENBs 120 to 128 each include a control protocol, such as Radio Resource Control (RRC), and generally control multiple cells.
A random access process is performed between a UE, which is in an RRC idle mode or an RRC connected mode, and an ENB, which is in a network node.
During a conventional random access process, the UE performs uplink timing synchronization with the ENB for (initial) uplink message/data transmission, sets initial uplink transmit power, or transmits a request for radio resource allocation for the (initial) uplink message/data transmission to the ENB.
When the UE is in the RRC idle mode, an anchor node or an upper node of the ENB, rather than the ENB itself, manages a location of the UE. The anchor node or upper node manages the location of the UE not on a cell basis but on a tracking area basis for paging, using context information of the UE.
If both the anchor node and the ENB set up an RRC connection between the UE and the ENB using the context information of the UE, the UE enters the RRC connected mode. Then, the ENB manages the location of the UE that has entered the RRC connected node on a cell basis.
FIG. 2 is a signal flow diagram illustrating a conventional random access process.
Referring to FIG. 2, in step 221, a UE 210 triggers a random access process with an ENB 211. For example, the UE 210 may perform the triggering in the RRC idle mode to inform the ENB 211 of the necessity of transmitting an uplink control message to start call setup.
The uplink control message is used to allow the ENB 211 to perform an operation of setting up an RRC connection to the UE 210 using context information of the UE 210 and transmitting a service request to an anchor node.
In step 231, the UE 210 randomly selects one of N preset random access preambles for transmission to the ENB 211. In step 241, the UE 210 transmits the selected random access preamble to the ENB 211 by using a preset Random Access Channel (RACH) for a predetermined time.
In step 242, the ENB 211 transmits the UE 210 a response message to the random access preamble received in step 241. To be more specific, the ENB 211 checks the random access preamble received from the UE 210, and allocates a Temporary Cell Radio Network Temporary Identifier (Temp_C_RNTI) to the UE 210. Although not illustrated, the ENB 211 respectively allocates a Temp_C_RNTI to each of multiple UEs to temporarily distinguish the multiple UEs that have transmitted a random access preamble, including the UE 210.
The Temp_C_RNTI that is allocated to the UE 210 is transmitted to the UE 210. Furthermore, although not illustrated, other Temp_C_RNTIs, that are respectively allocated to other UEs that have transmitted random access preambles, are transmitted to the other UEs. The Temp_C_RNTIs, including the Temp_C_RNTI transmitted to the UE 210, are transmitted over a physical downlink shared channel. The ENB 211 transmits radio resource allocation information for transmission of an uplink message to the UEs, together with the Temp_C_RNTI.
In step 251, the UE 210 checks the allocated Temp_C_RNTI, and transmits an RRC connection request message to the ENB 211 based on the allocated radio resource information. The RRC connection request message is forwarded to an RRC layer 212 with a control protocol for call setup control of the UE 210.
In step 253, the RRC layer 212 checks the Temp_C_RNTI and a channel status of the UE 210, and, if a call setup request condition is satisfied, the RRC layer 212 transmits a UE (call) setup response message to the ENB 211, thus completing the call setup. The RRC layer 212 uses the Temp_C_RNTI as a Cell Radio Network Temporary Identifier (C_RNTI) to distinguish multiple call setup-completed UEs in the cell.
In step 254, upon receiving the UE setup response message from the RRC layer 212, the ENB 211 uses the Temp_C_RNTI allocated to the UE 210 as a C_RNTI. In the future, the ENB 211 manages the UE 210 using the C_RNTI.
The ENB 211 should continuously store and manage the allocated Temp_C_RNTI until it receives the UE setup response message from the RRC layer 212.
In implementation of the above described system, however, the number of identifiers the ENB 211 can use to identify multiple UEs, that is, the number of Temp_C_RNTIs, is limited.
Accordingly, when the number of UEs simultaneously attempting to access the ENB 211 exceeds the number of available Temp_C_RNTIs, the ENB 211 may not allocate Temp_C_RNTIs to all of the UEs attempting the access. That is, because of the limited number of resources for allocating Temp_C_RNTIs, the ENB 211 may be unable to continuously allocate Temp_C_RNTIs.
An inefficiency of the above described system is that the ENB 211 continuously allocates a Temp_C_RNTI for a particular UE even when no RRC connection is set up between the UE 210 and the ENB 211 or when the ENB 211 has not received a UE setup response message from the RRC layer 212.
Therefore, a method for efficiently using the limited number of Temp_C_RNTIs is needed. In other words, there is a demand for a method of more efficiently allocating Temp_C_RNTIs taking the current resource allocation of the ENB into consideration. In addition, a more efficient random access method for addressing such problems is needed in a mobile communication system.